Heat detection sensor



May 31, 1966 J. E. LINDBERG, JR

HEAT DETECTION SENSOR Filed March 9, 1961 FIRESTATION 1 l l ll h R6 mm 2 W N/ I G v F 1. M :2 o 6 J \n4/ p A QF L. M J k 5 f g, 3 ,3 w M a w (a a 7 4 m 3 3 A n 3 an a.

m 2 3 gm I F United States Patent 3,253,572 HEAT DETECTION SENSOR John E. Lindherg, IL, 1170 Oleander Drive, Lafayette, Calif. Filed Mar. 9, 1961, Ser. No. 94,572 6 Claims. (Cl. 116-1145) This invention relates to improvements in heat detection and especially fire detection. This application is a continuation-in-part of application Serial No. 815,406, filed May 25, 1959, now US. Patent 3,122,728.

The invention is characterized by its provision of a novel non-electric heat-detecting element or sensor. Only this detecting sensor need be located in a fire zone (or other heat-detection zone), and it is connected, preferably outside the zone, to an electrical warning or corrective system, preferably by a pressure-sensitive instrument that I term a responder. The responder may most conveniently be located outside the zone in which detection is desired, though usually close to it. The actual alarm or heat-condition indicator can be connected to the responder by a wire of practically any desired length. For example, the non-electric heat-detecting sensor may be inside a house, the responder just outside the house, and the indicator at the fire station.

Furthermore, the novel heat-detecting sensor may be wire-like,a long, very-narrow-diameter, hollow tube. It i may extend along a line, around a circle, or along any desired path and for quite a considerable length. The invention is useful for detecting fire or overheat conditions at any point in any vehicle or building, and has numerous commercial and industrial applications.

False alarms have plagued heat and fire-detecting systems relying on electrical circuits extending into the fire zone. For example, moisture condensation has often caused electrical fire detectors to develop low-resistance shorts that resulted in false alarms. The present invention solves the problem of preventing moisture and other atmospheric conditions from causing false alarms, and it does this by using a sensor that is never actuated by moisture or by atmospheric conditions, and by using a low-impedance circuit.

This invention also eliminates other factors that'led to false alarms or failures in prior-art devices. Such problems as moisture condensation in voids at the joints between successive elements of continuous-type detectors and the accumulation of foreign material in the connections, both leading to low resistance shunt paths between the inner conductor and the outer shell and hence to false warning, cannot occur in this invention. My invention uses only the simplest electrical connection and normally locates that connection at or behind the fire wall where it is well protected.

An outstanding feature of the invention is that the warning circuit can be operated at an impedance of less than one ohm. This feature greatly increases the reliability of the system, for this impedance is so low that complete immersion of the circuit in Water does not seriously affect its operation.

Some priorart types of fire detectors have given false alarms because they responded to the rate of change of temperature rather than, or in addition to, a predetermined high temperature level. The device of this invention can be made independent of the rate of change of temperature or can be made to have any desired degree of dependence on it; so another source of false alarms is obviated.

Prior-art continuous-type fire detectors also gave false alarms whenever the detector element was seriously damaged, because short circuits were then caused within the element. The sensor of the present invention can be completely severed, cut open, dented, or bent in any fashion without causing a false alarm.

A further object is to provide a simple one-shot fire detector.

Another object is to provide a fire-detection system which avoids the complexities characteristic of the circuits and mechanical elements of other fire detectors. For example, no amplifiers or relays need be used in this system.

Another object is to provide a completely hermetically sealed heat-detection transducer, entirely free from environmental errors caused by such things as pressure changes, moisture condensation, and so on.

Other objects and advantages of the invention will appear from the following description of several preferred embodiments thereof.

In the drawings:

FIG. 1 is a diagrammatic view in elevation of a firedetection system embodying the principles of this invention, so installed as to detect fire in a house and give an alarm in a fire station, when and if fire does occur in the house. The broken line in the conductor indicates that the distance between the house and the fire station is not shown and can be any such distance as is commonly encountered.

FIG. 2 is an enlarged view in elevation and in section of a simplified form'of fire-detection system, as may be used in the FIG. 1 system. It shows the responder and a heat-detection sensor that is broken in the middle to conserve space. The electrical circuit is shown diagrammatically.

FIG. 3 is a greatly enlarged view in elevation and in section of a portion of a preferredform of a heatdetection sensor of this invention.

A. GENERAL STATEMENT OF THE INVENTION As shown in FIG. 1, the fire-detection system of this invention comprises (1) a non-electric detection means, preferably in the form of a generally Wire-like sensor A of indeterminate length, (2) a responder B, and (3) an electrical circuit C. The function of the sensor A is to actuate the responder B, and the function of the responder B is to actuate the electrical circuit C in response to predetermined conditions of temperature obtaining in the environment within which the sensor A is located. Thus, the sensor A and the responder B, considered together, comprise a transducer.

The sensor A may be further defined in general terms (see FIG. 3) as a generally wire-like enclosure D of extended length connected to the responder B and containing means E responsive to heat in the environment of the sensor A, for raising the pressure in the responder B. The responder B may be thought of as typically a pressure-actuated electrical switch that opens or closes the electrical circuit C in response to pressure changes induced by the sensor A as a result of the effect of temperature on the sensor A. The electrical circuit C may be a warning circuit or a remedial circuit. Several responders B may be used in one circuit, if desired, to control it in some manner that depends on the temperature of the environments to which the sensors A are exposed.

B. A HOME INSTALLATION (FIG. 1)

The fire-detector system of this invention may be used to give instant alarm in a first station when there is a fire in a home. For example, as shown in FIG. 1, the detector element or sensor A may be disposed along critical locations in John Does house 10; such as in an attic 11, immediately beneath and above a ceiling 12, down one or more walls 13, and along one or more fioors 14. As will be shown presently, the sensor A may comprise a thin, generally wire-like tube and may be quite inconspicuous when installed.

The responder B may be located just outside the house and is an actuator that closes an electrical circuit C,,

none of which extends inside the house 10. The circuit C includes a conductor 15, such as copper wire that leads to an alarm panel 16 in a fire station 17. The circuit C may have its power supply 18 located in the fire station 17. The panel 16 may include a bell or buzzer or other audible warning (not shown) as well as a signal light 19 identifying the house 10 as John Does house. There may be as many lights 19 on the panel 16 as there are homes having the Warning system installed; so each house can be instantly identified.

When a fire occurs in John Does house 10, the sensor A is heated. In a manner explained later, the rise in temperature increases the pressure inside the sensor A,

and this pressure acts on the responder B almost instantaneously, closing the circuit C (in a manner also explained later). Upon closure of the circuit C, current flows through the conductor and lights the light 19, also giving audible warning if desired. The men in the fire station can take immediate remedial action to save John Does house.

C. DETAILED DESCRIPTION OF SOME PRE- FERRED FORMS OF THE SYSTEM AND ITS COMPONENTS (1) The sensor A The fire detector of this invention includes a novel detecting means or sensor A. The sensor A has a gastight enclosure D, preferably comprising a narrow-diameter metal tube of constant cross-sectional area and of any desired length. Within this enclosure D is means E responsive to the temperature of the enclosure D for varying the pressure inside the enclosure D. The only opening in the enclosure D is connected to the responder B, which itself defines a closed chamber connected to the enclosure D. An alteration of the internal pressure within the enclosure D therefore affects the responder B.

(a) THE TRANSDUCING AGENT E This invention depends, in most aspects, upon the ability of certain classes of substances known as blowing agents, to release or liberate large volumes of gas or vapor when elevated to a temperature sought to be detected. In this specification, the term blowing agent means those solids that non-explosively decompose irreversibly, when heated, into a large amount of gas. When these blowing agents are employed as the means E and are enclosed in a constant-volume container D and subjected to an increase in temperature, the resultant change in the internal pressure of the container D is employed to actuate the responder B to close or open a warning sys-' tern C.

Heretofore, the blowing agents have been almost solely used in the manufacture of sponge rubber and foam plastic. Typical blowing agents are:

(a) Celogen, a white crystalline powder with a specific gravity of 1.56 that decomposes. at about 151 C. to 156 C., liberating about 105 to 110 cc. of non-condensible gas per gram of powder, 98.45% of the gas being nitrogen. Chemically, Celogen is p, p oxy bis (benzene sulfonyl hydrazide).

(b) Unicel ND, a white powder that decomposes at 180 C. to 190 C., liberating about 116 cc. of gas per gram of powder, 90 to 95% of the gas being nitrogen. Chemically, Unicel ND is dinitrosopentamethylenetetrarnine.

(c) Porofor DB (diazoaminobenzene).

(d) Wingcel S (p-tert-butylbenzoylazide).

(e) Porofor N (azocyano methane).

(f) Porofor BSH (benzene sulfonyl hydrazide).

These blowing agents are useful for one shot or noncyclical processes. Their process of gas liberation is classified as irreversible, for once the gas has been released, it cannot be recombined with the remaining solids except under the most extreme treatment. A blowing agent may be enclosed within a rigid container D, then when heat is applied to elevate the substance E to its triggering temperature, the subsequent release of gas raises the internal pressure of the container D quite sharply.

These materials, when located within a closed chamber, provide an effective means of altering the internal pressure of the chamber as a function of the temperature applied to the material. Thus, the enclosed blowing agents function to effectively convert temperature variations into pressure variations, and that is why they are referred to herein as transducing agents.

(1)) TYPICAL SENSOR STRUCTURES FIG. 3 illustrates one of the ways in which the sensor A may be constructed. The blowing agent E may be used in a pellet form or some other .suitable form, always being placed inside the sensor tube D which may be a nonporous tube of constant cross-sectional area. In all cases there has to be passage means for transmitting the pressure changes along the tube. In applications where the tubes D are to be bent or curved around corners, metal is the preferred material. Suitable metals are pure iron, which is impermeable to many gases, stainless steel, and molybdenum, for example. In applications where bending is not required and minimum diffusion is desired, the tube D is preferably made from non-porous quartz, ceramic, or special glass. In any event, the inner surface of the tube D should not react with the materials it contacts, including the gas involved. A typical sensor tube D is preferably about .030 to 0.060" outside diameter with a wall thickness of preferably about 0.005" to 0.015". Such tubes D are preferably about one to forty feet long, although they may be longer or shorter.

FIG. 3 shows a preferred form of blowing agent E enclosed in the sensor tube D. Here the blowing agent E is in the form of a series of pellets 20 such as Celogen. The pellets 20 are smaller than the bore 21 of the tube E, the space 22 between the wall 21 and the pellets 20 providing passage means for the gas along the tube.

As a simplified example of installation of the sensor A of FIG. 3 to the responder B, one end 23 (FIG. 2) of the tube D may be connected by a gas-tight seal to the responder B, while the other end 24 of the tube D is still open. This free end 24 may be connected to a vacuum pump and the tube D pumped free of undesired gas. Then it may, if desired, be filled with any desired gas or left evacuated. The free end 24 is then sealed off, and the device is ready for operation.

(2) A simple form of responder B (FIG. 2)

Any pressure switch that is properly sensitive and has the needed connections may be used as a responder B. However, I have invented a new pressure switch that is especially suitable for use herein. This switch is fully disclosed and claimed in a co-pending patent application, Serial No. 86,252, filed April 10, 1961, now US. Patent No. 3,180,956.

FIG. 2 shows a simple form of responder B, suitable for simple installations such as are shown in FIGS. 1-3. This responder B comprises a unit 25 and has two circular plates 26 and 27, preferably of non-porous metal, between which is bonded (as by brazing) a thin metal flexible disc or diaphragm 28. The plates 26 and 27 are hermetically sealed together and are in electrical contact for their full peripheries and over a substantial margin, but in the center the diaphragm 28 has a generally spherical depression 30 called a blister, which is free to move relative to the plates 26 and 27 and constitutes the active or movable part of the diaphragm 28. Use of a diaphragm with a blister 30 makes possible the use of an upper plate 27 with a planar lower surface 31 and gives a more pred-' icatable response, but other diaphragm structures may be used where feasible. The lower plate 26 is formed with a recess 32 in its upper surfaces and the diaphragm 28 divides the resultant cavity between the plates into two regions or chambers 33 and 34. Since the lower region 33 communicates with the sensor A, it may be called the sensor chamber. The other region 34 is located on the opposite side of the diaphragm 28 from the sensor A; so it may be called the anti-sensor chamber. Of course, either plate 26 or 27 may actually be made by brazing together several thin plates of the desired configuration, and the recess 30 may be provided by using a stack of preformed thin washers over a disc. The end 23 of the sensor tube D is joined to and sealed to the lower plate 26, fitting within a hole 35. The region 33 is closed and sealed except for its communication with the lumen of the sensor tube D.

A tube 36 of non-porous ceramic material or other non-porous electrically-insulating material extends through an opening 37 in the upper plate 27 and is hermetically sealed in place there with its lower end 38 flush with the bottom surface 31 of the plate 27. The hole 37 and tube 36 are preferably centered with respect to the blister 30, on the anti-sensor side thereof. A metal electrode 40 is located inside and joined securely to the tube 36 at the end 38 nearest the blister 30, with a portion 41 of the electrode 40'extending below the lower surface 31 of the plate 27. The amount by which the portion 41 extends below the surface 31 is carefully controlled so as to be uniform in each responder of any particular design. This geometry means that the blister 30 can make electrical contact with the electrode portion 41 when the blister 30 is forced up by pressure in the sensor chamber 33. As shown, the electrode 40 may be annular to give good uniform contact with the blister 30 at that time and also to afford communication between the chamber 34 and the inside 42 of the tube 36. A conducting wire 43 extends from the electrode 36, preferably along the axis of the tube 40, and is brought out of the tube 36 through a hermetic seal at a sealing cap 44. The tube interior 42 and the anti-sensor chamber 34 thus are part of the same enclosure.

If sufiicient pressure is applied to the sensor side of the blister 30, it will deflect and make contact with the electrode portion 41; and if the deflecting force is removed, the restoring force of the blister 30 will return it to its relaxed position and thus break contact with the electrode portion 41. The force necessary to do this may be chosen by proper design of the blister to accommodate a wide range of values.

(3) A simple circuit C and its operation (FIG. 2)

As explained before, the responder B may be connected to an alarm circuit which, as shown in FIG. 2, may be a simple visual indicator consisting of a lamp 45 in series with the conducting wire 43 and a source 46 of electrical current, which may be a battery, as shown, or may be a source of alternating current. A return path for the electrical circuit C may be provided by grounding either one of the plates 26 or 27 and is shown as a ground wire 47 in FIG. 2.

In operation, when the sensor A is exposed to heat at a level high enough to cause the blowing agent E to rise above its threshold temperature, gas is liberated. This.

gas cannot escape from the sensor tube D except into the sensor chamber 33, where it exerts pressure upon the blister 30. This pressure tends to move the blister 30 away from the plate 26 and toward the plate 27. The pressure in the sensor chamber 33 is a function of the temperature of the sensor A. This pressure, if great enough, will cause the blister 30 to make contact with the electrode 40, but no contact will be made unless the temperature of the sensor A is at or above a definite level.

When the sensor A is exposed to heat at a level high enough to cause the blister 30 to make contact with the electrode 40, current flows from the battery 46 through the lamp 45, the conductor 43, the electrode 40, and

the blister 30 to the plates 26 and 27 and returns to the battery 46 through the ground line 47. This current flow causes the lamp 45 to light and provides a visual indication that the temperature of the sensor A is at or above a certain level. in FIG. 2 functions as a threshold temperature indicator. When heat is removed from the sensor A, the blowing agent E will not reabsorb its previously liberated gas; it is a one-shot device. The alarm stays on until remedial action is taken.

In practice, the sensor A is placed in the area (see FIG. 1) whose temperature is to be monitored, while the responder B may be located upon or behind a shielded wall or at some easily accessible area. Thus only the sensor A itself need be exposed to possible heat sources, and it contains no element of the electrical warning circuit. In this manner, protection for the responder B and its associated alarm circuit C may be provided.

(4) Some ways of setting the threshold temperature (FIG. 2

The force necessary to deflect the blister 30 against the electrode 40 can be chosen to accommodate a range of values by a suitable choice of mechanical parameters. Once this force is determined, the dimensions of the sensor tube D and the amount of blowing agent B may be chosen by design to provide the force necessary to obtain contact between the blister 30 and electrode 40 under desired conditions.

In addition to mechanical design considerations, the necessary deflecting force may also be altered by precharging the anti-sensor chamber 34 with a gas under pressure or by partially evacuating it. To accomplish this, gas is forced into (or withdrawn from) the tube 36 after its attachment to the plate 27 and before it is closed by its cap 44. The required deflecting pressure against the blister 30 becomes greater as more gas is present in the chamber 34.

Alternatively, the deflecting pressure may be effectively lowered by precharging the inside of the sensor tube D and the sensor chamber 33 with gas. In this case, if the ambient pressure in the sensor chamber 33 is greater than normal, less than normal gaseous liberation from the transducing agent E is required to deflect the blister 30 against the electrode 40. Most gases may be employed for this purpose; however, ideally the gas should not react chemically with its surrounding materials. Particularly suitable are the inert gases, such as helium, argon, neon, and xenon, (the helium family, known as the noble gases) especially since they do not readily diffuse through most materials. As a consequence, a precharged pressure of argon, for example, may be maintained for an indefinite length of time to retain a desired biasing of the diaphragm 28, as described.

Celogen will serve as an example of the blowing agent E. When a sensor A containing Celogen as the transducing agent E is exposed to a heat level of 156 C. (313 F.), the Celogen decomposes and deflects the blister 30 against the electrode 40, thereby actuating the alarm circuit C. The reaction is irreversible; when the sensor A cools, the released gas is not reabsorbed, so the lamp 45 remains illuminated until the circuit C is externally opened. However, this one shot operation is desirable in some cases; for example, in a house fire alarm, as in FIG. 1. To monitor temperature again, the used sensor may be replaced with a new one or refilled with new Celogen.

With blowing agents, locally applied heat at or above the triggering temperature causes the liberation of gas. The material not exposed to heat will not liberate gas, but also it will not absorb the gas liberated from the In this sense, the device shown 4 hotter portion; as a result, any liberated gas increases the pressure in the sensor chamber of the responder B.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. A continuous-type heat sensor comprising an imperforate narrow diameter wire-like generally tubular enclosure, a blowing agent, comprising a solid that irreversibly and non-explosively decomposes when heated into large volumes of gas, disposed substantially uniformly in and along substantially the full length of said enclosure, means providing continuous passage for gas throughsaid enclosure and pressure responsive means positioned at a predetermined portion of said enclosure.

2. The sensor of claim 1 wherein said passage is filled with noble gas.

3. The sensor of claim 1 wherein said blowing agent comprises chunks placed in said enclosure loosely enough to afford said passage means.

4. The sensor of claim 1 wherein said blowing agent is disposed continuously along substantially the full length of said tube.

5. The sensor of claim 1 wherein a plurality of portions of said tube are filled with said blowing agent and these portions are separated by. gaps.

6. The sensor of claim 5 wherein the said blowing agents used in some portions are of different type from the said blowing agents used in other portions.

References Cited by the Examiner UNITED STATES PATENTS 436,045 9/ 1-890 McElroy 200-140 X 466,761 1/1892 Wotton 200 X 2,271,307 1/1942 Ray 73368.2 X 2,764,599 9/1956 Clifford et al 2602.5 2,766,229 10/1956 Hardy et a1. 2602.5 2,778,818 1/1957 Hyson et al. 2602.5 2,788,333 4/1957 'Lewis et al. 2602.5 3,064,245 11/1962 Lindberg 340227 3,122,728 2/1964 Lindberg 73368 3,177,479 4/1965 Lindberg 200- 3,180,956 4/196'5 Lindberg 200140 FOREIGN PATENTS 11,393 3/1914 Great Britain. of 1913 OTHER REFERENCES Journal of Chemical Education, October 1948. Report of the New England Association of Chemistry Teachers, Hydrides, pages 577-582, Gibbs, J r.

Comprehensive Inorganic Chemistry, vol. 6, Sneed, M.C., et al., D. Van Nostrand Co., Inc., pages l12117.

LOUIS J. CAPOZI, Primary Examiner.

NEIL C. READ, Examiner. 

1. A CONTINUOUS-TYPE HEAT SENSOR COMPRISING AN IMPERFORATE NARROW DIAMETER WIRE-LIKE GENERALLY TUBULAR ENCLOSURE, A BLOWING AGENT, COMPRISING A SOLID THAT IRREVERSIBLY AND NON-EXPLOSIVELY DECOMPOSES WHEN HEATED INTO LARGE VOLUMES OF GAS, DISPOSED SUBSTANTIALLY UNIFORMLY IN AND ALONG SUBSTANTIALLY THE FULL LENGTH OF SAID ENCLOSURE, MEANS PROVIDING CONTINUOUS PASSAGE FOR GAS THROUGH SAID 